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Fries Rearrangement

Fries Rearrangement   Named Reactions in Organic Synthesis
Reaction category:
Electrophilic aromatic substitution

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In the early 1900s, K. Fries and colleagues reacted phenolic esters of acetic and chloroacetic acid with aluminium chloride isolating a mixture of ortho and para-acetyl and chloroacetyl phenols. Fries realized that this rearrangement of phenolic esters was general and for this the transformation of phenolic esters to corresponding ketones and aldehydes in the presence of Lewis or Bronsted acids (e.g. HF; HClO4; PPA) became known as the Fries rearrangement.

There are two main types of Fries rearrangement, the first an anionic reaction where ortho-lithiated O-aryl carbamates are converted to substituted salicylamides, and a photochemical reaction where light-irradiated  phenolic esters are converted to the corresponding phenols.

The Friedel-Crafts acylation of phenols is often a two-stage process, formation of the phenolic ester followed by a Fries rearrangement.

Mechanism of the Photo-Fries Rearrangement

Photo-Fries Rearrangement Mechanism

One application of the Fries rearrangement is in the synthesis of the potent protein kinase C inhibitor (-)-balanol.

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Some relevant Alfa Aesar products for the Fries rearrangement: Lewis and Bronsted acids
Hydrofluoric acid, ACS, 48-51%
Hydrofluoric acid, 99.99% (metals basis) 40% min
Perchloric acid, 70% aq. soln.
Perchloric acid, ACS, 48-50%
Perchloric acid, ACS, 60-62%
Perchloric acid, 70%, 99.9985% (metals basis)
Perchloric acid, 0.1N in Acetic Acid Standardized Solution
Polyphosphoric acid, ca 84% (as phosphorus pentoxide)


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